对生物体内几类核苷分子激发态淬灭机理的理论研究

As the genetic material, the stability of DNA and RNA are crucial for the survival of organism. As a result of the nature selection during a long period of molecular evolution, DNA and RNA can keep stable inheritance after a perennial exposure to the UV in the sunlight. Such photostability is related with the intrinsic photophysical properties of the DNA and RNA building blocks such as bases, nucleosides and nucleotides. To date, numerous experimental and theoretical studies have been undertaken to investigate the excited state decay mechanism of the DNA and RNA bases and reveal the underlying mechanism. Given that studies of nucleosides are a natural next step in bottom-up understanding of DNA and RNA photophysics, it is surprising that little theoretical work have been undertaken by far. It has been proposed that the deactivation pathways of nucleosides are different from those of the isolated bases. In the current project, we will combine the high-level quantum chemical calculations with non-adiabatic dynamical simulation method to investigate the excited state dynamical behavior of the adenosine, guanosine, cytidine and thymidine. In addition, we will further investigate the effect of solutions on dynamical behavior of nucleosides, and the competition between the intermolecular and intramolecular hydrogen bonding. The present work could be helpful to give a comprehensive understanding of the DNA and RNA photostability and provide theoretical guides for further design of biomimetic materials.

DNA和RNA做为生物体的遗传物质，其稳定性对生物体的生存繁衍至关重要。经过长期的自然选择，DNA、RNA分子在长期受到太阳光中紫外线照射后仍能稳定遗传，这与组成其结构的碱基，核苷（酸）固有的光物理性质密不可分。目前对碱基分子的激发态淬灭机理已经研究的比较详细。做为“由下至上”研究DNA、RNA 光稳定性的下一步，人们对核苷分子的光物理性质研究却很少。实验发现核苷与碱基分子的激发态淬灭路径不同，本项目拟利用静态的量化计算结合非绝热动力学模拟的手段，深入研究腺苷、鸟苷、胞苷以及胸苷四类分子的激发态动力学行为，详细的阐明其退激发机理。并进一步探究溶液环境对其动力学行为的影响，研究分子间氢键与分子内氢键之间的相互竞争机制。本项目的完成将有助于人们更加全面的了解DNA、RNA光稳定性的本质原因，并为设计仿生光稳定性材料提供理论指导。

DNA与RNA分子因其特殊的光化学物理性质使其在长期接受紫外线照射后仍能稳定遗传，这种性质与组成其结构的基本单元碱基及核苷（酸）的激发态动力学行为密不可分。因此对这些结构单元的激发态动力学性质进行详细的研究，有助于人们更加全面的了解DNA与RNA光稳定性的本质原因，并为合理设计仿生光稳定材料提供理论指导。目前，人们的研究对象主要集中在结构相对简单的碱基上，而对于结构相对复杂的核苷分子研究很少。本项目利用高精度的电子结构计算结合激发态非绝热动力学模拟的手段，系统的研究了多个核苷分子的激发态动力学行为，给出了完整的退激发图像，计算结果发现不同核苷分子的激发态动力学行为是各具特点的，不能一概而论。在腺苷分子中发现的通过激发态质子转移过程完成退激发的现象在胞苷、尿苷及鸟苷中没有发现，它们的退激发通道主要集中在碱基部分的结构变化上，而且五碳糖结构的加入使得核苷分子与对应碱基分子的激发态动力学性质有所不同。在此基础上，我们还进一步探索了取代基对一系列天然与非天然碱基光化学和光物理性质的影响，给出了详细的退激发机理，为研究利用取代基调控分子的光化学物理性质提供了理论依据。本项目的研究成果为实验现象提供了合理的解释，细化或弥补了实验研究的不足，也充分说明了理论研究重要性。